The agricultural and other industries routinely use hitches capable of movement in the horizontal and vertical directions. A work implement, such as a cultivator, is attached to a hitch, which is in turn attached to a work machine, such as a tractor. The horizontal movement of the hitch allows for articulation between the cultivator and the tractor. The vertical movement of the hitch allows for the cultivator to be raised out of and off the ground. This typically occurs when the tractor is traveling between fields or on a road.
As the hitch is raised, it is important to center the hitch relative to the tractor. If the hitch is not centered as it is raised, it will exert a torque that tends to urge the tractor into a roll. Although the torque is typically orders of magnitude less than the torque required to roll a tractor, the torque nonetheless makes the tractor less stable than if it were not present. In addition, when the hitch is off-center as it is raised, it may contact other components on the tractor, such as a power take off or implement valve stack, causing wear or damage.
In the past, mechanical guides, such as sway blocks, have been used to force the hitch toward center as it raises. The sway blocks form a physical barrier beyond which the hitch cannot travel. Sway blocks however, present several problems. For example, when the hitch encounters a sway block, significant rubbing between the hitch and sway block occurs. This wears both the hitch and sway block, causing the need for frequent repair and replacement of both pieces. In the past, conventional hitches were generally free moving, and do not experience significant problems with rubbing. However, many hitches today now hold the hitch hydraulically in a given position, even when being raised, thus causing the significant rubbing mentioned above. In addition, when hydraulic cylinders are used to move the hitch, the resistance of the sway blocks to the motion of the hitch can cause significant backpressure in the hydraulics.